Mammogram Dilemma: Screening Depends on Personal Risk

A new review of 50 years’ worth of studies assessing the value of mammograms finds that the benefits are often overstated, the harms are minimized — and that decisions about screening must be tailored to individual risks and personal preferences.

In other words, women should talk with their doctors to understand whether and when to undergo the screenings aimed at detecting breast cancer, which kills 40,000 American women a year. That's according to the study, published Tuesday in JAMA, which aims to clear up ongoing confusion about the familiar tests.

“What I tell my patients is that mammogram is not a perfect test,” said Dr. Nancy Keating of Harvard Medical School and Brigham and Women's Hospital and co-author of the new review. “Some cancers will be missed, some people will die of breast cancer regardless of whether they have a mammogram and a small number of people that might have died of breast cancer without screening will have their lives saved.”

The debate about the value of mammograms has raged since 2009, when the U.S. Preventive Services Task Force dramatically altered its recommendations, saying that women should get regular screenings starting at age 50, not 40, as was previously advised.

For the new review, Keating and her colleagues searched MEDLINE, a massive database complied by the U.S. National Library of Medicine, for studies assessing mammography from 1960 through 2014. They looked at data from eight large randomized controlled trials conducted during that period.

They found that mammography screening was associated with a 19 percent overall reduction in the risk of dying from breast cancer, with about 15 percent reduction for women in their 40s and about 32 percent for women in their 60s.

"If, for example, we took 10,000 women who were age 40 and they received mammograms every year for 10 years, over that time, about 190 of those 10,000 women would be diagnosed with breast cancer," Keating told NBC News. "About 30 would die of breast cancer, regardless of screening. And only five women will have their lives saved by the mammogram."

But whether and how much a woman actually benefits depends on her personal risk of breast cancer — and all women share the risk of overdiagnosis, the authors found. For a 40- to 50-year-old woman undergoing 10 years of regular mammograms, more than 60 percent could expect a false positive exam. In addition, about 19 percent of cancers detected would not have become apparent without screening, Keating said. That means that 36 of 190 women who got regular mammograms for 10 years would be subjected to unnecessary surgery, chemotherapy or radiation.

In an editorial accompanying the study, Dr. Joann Elmore of the University of Washington School of Medicine in Seattle and Dr. Barnett Kramer of the National Cancer Institute stress that health workers should help women cut through the confusion.

“Balanced messaging is essential to help each woman make her own individual decision regarding her participation is screening mammography,” they wrote.